Enhanced Lithium Ion Battery Cycling of Silicon Nanowire
Anodes by Template Growth to Eliminate Silicon Underlayer Islands
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Abstract
It
is well-known that one-dimensional nanostructures reduce pulverization
of silicon (Si)-based anode materials during Li ion cycling because
they allow lateral relaxation. However, even with improved designs,
Si nanowire-based structures still exhibit limited cycling stability
for extended numbers of cycles, with the specific capacity retention
with cycling not showing significant improvements over commercial
carbon-based anode materials. We have found that one important reason
for the lack of long cycling stability can be the presence of milli-
and microscale Si islands which typically form under nanowire arrays
during their growth. Stress buildup in these Si island underlayers
with cycling results in cracking, and the loss of specific capacity
for Si nanowire anodes, due to progressive loss of contact with current
collectors. We show that the formation of these parasitic Si islands
for Si nanowires grown directly on metal current collectors can be
avoided by growth through anodized aluminum oxide templates containing
a high density of sub-100 nm nanopores. Using this template approach
we demonstrate significantly enhanced cycling stability for Si nanowire-based
lithium-ion battery anodes, with retentions of more than ∼1000
mA·h/g discharge capacity over 1100 cycles